// This file is part of Eigen, a lightweight C++ template library
// for linear algebra.
//
// Copyright (C) 2012 Désiré Nuentsa-Wakam <desire.nuentsa_wakam@inria.fr>
//
// This Source Code Form is subject to the terms of the Mozilla
// Public License v. 2.0. If a copy of the MPL was not distributed
// with this file, You can obtain one at http://mozilla.org/MPL/2.0/.

/*

 * NOTE: This file is the modified version of [s,d,c,z]pruneL.c file in SuperLU

 * -- SuperLU routine (version 2.0) --
 * Univ. of California Berkeley, Xerox Palo Alto Research Center,
 * and Lawrence Berkeley National Lab.
 * November 15, 1997
 *
 * Copyright (c) 1994 by Xerox Corporation.  All rights reserved.
 *
 * THIS MATERIAL IS PROVIDED AS IS, WITH ABSOLUTELY NO WARRANTY
 * EXPRESSED OR IMPLIED.  ANY USE IS AT YOUR OWN RISK.
 *
 * Permission is hereby granted to use or copy this program for any
 * purpose, provided the above notices are retained on all copies.
 * Permission to modify the code and to distribute modified code is
 * granted, provided the above notices are retained, and a notice that
 * the code was modified is included with the above copyright notice.
 */
#ifndef SPARSELU_PRUNEL_H
#define SPARSELU_PRUNEL_H

namespace Eigen {
namespace internal {

/**
 * \brief Prunes the L-structure.
 *
 * It prunes the L-structure  of supernodes whose L-structure contains the current pivot row "pivrow"
 *
 *
 * \param jcol The current column of L
 * \param[in] perm_r Row permutation
 * \param[out] pivrow  The pivot row
 * \param nseg Number of segments
 * \param segrep
 * \param repfnz
 * \param[out] xprune
 * \param glu Global LU data
 *
 */
template<typename Scalar, typename StorageIndex>
void
SparseLUImpl<Scalar, StorageIndex>::pruneL(const Index jcol,
										   const IndexVector& perm_r,
										   const Index pivrow,
										   const Index nseg,
										   const IndexVector& segrep,
										   BlockIndexVector repfnz,
										   IndexVector& xprune,
										   GlobalLU_t& glu)
{
	// For each supernode-rep irep in U(*,j]
	Index jsupno = glu.supno(jcol);
	Index i, irep, irep1;
	bool movnum, do_prune = false;
	Index kmin = 0, kmax = 0, minloc, maxloc, krow;
	for (i = 0; i < nseg; i++) {
		irep = segrep(i);
		irep1 = irep + 1;
		do_prune = false;

		// Don't prune with a zero U-segment
		if (repfnz(irep) == emptyIdxLU)
			continue;

		// If a snode overlaps with the next panel, then the U-segment
		// is fragmented into two parts -- irep and irep1. We should let
		// pruning occur at the rep-column in irep1s snode.
		if (glu.supno(irep) == glu.supno(irep1))
			continue; // don't prune

		// If it has not been pruned & it has a nonz in row L(pivrow,i)
		if (glu.supno(irep) != jsupno) {
			if (xprune(irep) >= glu.xlsub(irep1)) {
				kmin = glu.xlsub(irep);
				kmax = glu.xlsub(irep1) - 1;
				for (krow = kmin; krow <= kmax; krow++) {
					if (glu.lsub(krow) == pivrow) {
						do_prune = true;
						break;
					}
				}
			}

			if (do_prune) {
				// do a quicksort-type partition
				// movnum=true means that the num values have to be exchanged
				movnum = false;
				if (irep == glu.xsup(glu.supno(irep))) // Snode of size 1
					movnum = true;

				while (kmin <= kmax) {
					if (perm_r(glu.lsub(kmax)) == emptyIdxLU)
						kmax--;
					else if (perm_r(glu.lsub(kmin)) != emptyIdxLU)
						kmin++;
					else {
						// kmin below pivrow (not yet pivoted), and kmax
						// above pivrow: interchange the two suscripts
						std::swap(glu.lsub(kmin), glu.lsub(kmax));

						// If the supernode has only one column, then we
						// only keep one set of subscripts. For any subscript
						// intercnahge performed, similar interchange must be
						// done on the numerical values.
						if (movnum) {
							minloc = glu.xlusup(irep) + (kmin - glu.xlsub(irep));
							maxloc = glu.xlusup(irep) + (kmax - glu.xlsub(irep));
							std::swap(glu.lusup(minloc), glu.lusup(maxloc));
						}
						kmin++;
						kmax--;
					}
				} // end while

				xprune(irep) = StorageIndex(kmin); // Pruning
			}									   // end if do_prune
		}										   // end pruning
	}											   // End for each U-segment
}

} // end namespace internal
} // end namespace Eigen

#endif // SPARSELU_PRUNEL_H
